1. Technical Field of the Invention
The present invention relates to touch-controlled circuit apparatus for voltage selection, and more particularly, to a glass membrane touch-controlled circuit apparatus for use in control panels requiring high-temperature, scratch-resistant characteristics.
2. The Prior State of the Art
Touch-controlled circuit devices for voltage selection are used in control panels in many types of applications in both home and industry. For example, control panels which employ such devices are used in connection with computers, elevators, video games, audiovisual equipment, stereo equipment, kitchen appliances, telephone equipment and in many other kinds of applications.
Touch-controlled circuits for voltage selection generally fall into two categories. One type of touch-controlled circuitry employs membrane-type devices which may provide for a variety of different control functions such as on-off switches and/or potentiometers which can be used in connection with single or multiple axis outputs. Examples of such touch-controlled membrane circuit devices are illustrated, for example, in U.S. Pat. Nos. 4,494,105 and No. 4,444,998, both issued to V. Dean House.
In these types of touch-controlled membrane circuit devices, a flexible membrane constructed, for example, of polyester carries a conductive surface which is spaced from another conductive surface or from a resistive surface, depending upon whether the device is to be used as an on-off contact switch or as a voltage divider. By application of tactile pressure to the flexible membrane, the conductive surface may be made to contact the other conductive or resistive film so as to provide a voltage output in the form of either an on/off voltage or a voltage which is a function of the voltage divider.
This type of touch-controlled membrane circuit device is advantageous since it provides an effective, relatively simple, low-cost device which can be used in a control panel to provide multiple functions in connection with various kinds of on-off switching controls as well as voltage dividers used in single or multiple axis selection devices such as XY controllers and the like. However, this type of device is limited with respect to some kinds of applications. For example, for some kinds of appliances or other applications it is important for the control panel to be scratch-resistant. Since touch-controlled membrane circuit devices of the mentioned type utilize flexible membrane material which is relatively soft, such as polyester, these materials are not sufficiently scratch resistant. Other kinds of appliances and applications also require that the control panel in use be capable of withstanding high temperatures, which is also a distinct limitation with respect to the mentioned type of touch-controlled membrane circuit devices. For example, control panels on a kitchen stove or oven would fall into this type of requirement.
As a result, to date flexible, touch-controlled membrane-type circuit devices have not been used with much success in control panels where such high-temperature, scratch-resistant characteristics are required. Instead, the control panels for such applications have used high-temperature, hard, inflexible materials. Because such materials are inflexible, they have been used to provide capacitive switching controls. Since this type of capacitive switching panel can only be used in connection with on-off switching functions, such control panels have typically combined functions requiring voltage selection by means of a voltage divider by using more conventional potentiometers which are operated by rotating control knobs and the like. In the alternative, in place of such control knobs, some capacitive control panels have utilized digital technology to provide for variable settings when required.
While touch-controlled capacitive switching panels do permit high-temperature materials to be used, they also suffer from certain drawbacks in terms of increased complexity with respect to the circuitry required to process the capacitive signals generated by such device. Furthermore, such capacitive switch panels also suffer from the disadvantage that they are operated based on the capacitive coupling which is sensed when the control panel is touched by the user. Accordingly, if the user has a substance on his or her hands such as lotion or some other substance or if the control panel has a substance on it, that substance may interfere with the capacitive coupling, and hence resulting in an incorrect response of the control panel under such circumstances.